1. Field of the Invention
This invention generally relates to a scanning arrangement in a scanner operative for repetitively scanning indicia having parts of different light reflectivity, for example, bar code symbols, and, more particularly, to operating such a scanning arrangement at high speeds in single or multi-axis scan patterns.
2. Description of the Related Art
Various optical readers and optical scanners have been developed heretofore to optically read bar code symbols applied to objects in order to identify the object by optically reading the symbol thereon. The bar code symbol itself is a coded pattern comprised of a series of bars of various widths and spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting properties. The readers and scanners electro-optically decoded the coded patterns to multiple digit representations descriptive of the objects. Scanners of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 4,409,470; 4,808,804; 4,816,661; 4,816,660; and 4,871,904, all of said patents having been assigned to the same assignee as the instant invention and being hereby incorporated herein by reference.
As disclosed in the above-identified patents and applications, a particularly advantageous embodiment of such a scanner resided, inter alia, in emitting a light beam, preferably a laser beam, emitted from a light source, preferably a gas laser or a laser diode, and in directing the laser beam to a symbol to be read. En route to the symbol, the laser beam was directed to, and reflected off, a light reflector of a scanning component. The scanning component moved the reflector in a cyclical fashion and caused the laser beam to repetitively scan the symbol. The symbol reflected the laser beam incident thereon. A portion of the incident light reflected off the symbol was collected and detected by a detector component, e.g. a photodiode, of the scanner. The photodiode had a field of view, and the detected light over the field of view was decoded by electrical decode circuitry into data descriptive of the symbol for subsequent processing. The cyclically movable reflector swept the laser beam across the symbol and/or swept the field of view during scanning.
U.S. Pat. Nos. 4,387,297 and 4,496,831 disclose a high-speed scanning component including an electric motor operative for reciprocatingly oscillating a reflector in opposite circumferential directions relative to an output shaft of the motor. Electrical power is continuously applied to the motor during scanning. The light beam which impinges on the light reflector is rapidly swept across a symbol to be scanned in a predetermined cyclical manner. The scanning component comprises at least one scan means for sweeping the symbol along a predetermined direction (X-axis) lengthwise thereof. The scanning component may also comprise another scan means for sweeping the symbol along a transverse direction (Y-axis) which is substantially orthogonal to the predetermined direction, to thereby generate a raster-type scan pattern over the symbol. In addition to a single scan line and the raster-type pattern, other types of scan patterns are also possible, such as, x-shaped, Lissajous, curvilinear (see U.S. Pat. No. 4,871,904), etc. For example, if the X and Y axis scanning motors are both driven such that the light reflectors are driven at a sinusoidally-varying rate of speed, then the scan pattern at the reference plane will be a Lissajous-type pattern for omni-directional scanning of the symbols. The use of two separate scanning motors and control means to produce the multi-axis and omni-directional scanning pattern increases material and labor costs as well as the amount of electrical power needed to operate the scanner. In addition, the relatively complicated motor shaft and bearing arrangements of the scanning components may result in a useful life that is inadequate for some applications. Furthermore, the scanning components disclosed in U.S. Pat. Nos. 4,387,297 and 4,496,831 are designed for miniature light reflectors and are not well suited for large scale reflectors.